Corrosion resistant steel composition

ABSTRACT

A steel composition resistant to sulfidic corrosion has been discovered. The newly discovered steel composition comprises the elements Fe, C, Si, Cu, and Mn wherein the composition comprises from about 96.80 to about 99.00 percent by weight iron, from about 0.10 to about 0.30 percent by weight carbon, from about 0.20 to about 1.40 percent by weight silicon, from about 0.50 to about 1.50 percent by weight copper, and from about 0.20 to about 1.00 percent by weight manganese, wherein the composition is substantially free of chromium, and wherein the composition contains less than 0.1 percent by weight nickel, molybdenum, or tungsten.

This application describes and claims certain subject matter that wasdeveloped within the scope of a written joint research agreement betweenGeneral Electric Company and Chevron U.S.A., Inc., which was in effectprior to the inventive activities resulting in the present applicationand claims.

BACKGROUND

The present invention relates to corrosion resistant steel compositions.In particular the present invention relates to steel compositions whichresist corrosion in environments containing high levels of hydrogensulfide.

As the world's economies rely to an ever greater extent on hydrocarbonenergy resources containing relatively high levels of hydrogen sulfide,problems associated with hydrogen sulfide induced corrosion of steelcomponents of hydrocarbon refining operations represent growing risks topersonnel, plant equipment and the environment.

Although various approaches to inhibiting environmental corrosion ofsteel are known in the art, and many different steel compositions havebeen prepared and tested, there remains a need for relatively low coststeels which exhibit robust resistance to the corrosive effects ofhydrogen sulfide at high temperatures. This need is particularlypronounced in oil refining operations where hot fluids laden withhydrogen sulfide come into contact with steel surfaces, for example indistillation vessels, pipes and heat exchangers.

BRIEF DESCRIPTION

In accordance with one aspect of the present invention, a hydrogensulfide resistant steel composition is provided that includes theelements Fe, C, Si, Cu, and Mn wherein the composition comprises fromabout 96.80 to about 99.00 percent by weight iron, from about 0.10 toabout 0.30 percent by weight carbon, from about 0.20 to about 1.40percent by weight silicon, from about 0.50 to about 1.50 percent byweight copper, and from about 0.20 to about 1.00 percent by weightmanganese, wherein the composition is substantially free of chromium,and wherein the composition contains less than 0.1 percent by weightnickel, molybdenum, or tungsten.

In accordance with another aspect of the present invention, a hydrogensulfide resistant steel composition is provided that includes theelements Fe, C, Si, Cu, and Mn wherein the composition comprises fromabout 96.80 to about 99.00 percent by weight iron, from about 0.10 toabout 0.30 percent by weight carbon, from about 0.20 to about 0.40percent by weight silicon, from about 0.50 to about 1.50 percent byweight copper, and from about 0.20 to about 1.00 percent by weightmanganese, wherein the composition is substantially free of chromium andaluminum, and wherein the composition contains less than 0.1 percent byweight nickel, molybdenum, or tungsten.

In accordance with yet another aspect of the present invention, ahydrogen sulfide resistant steel composition is provided that includesthe elements Fe, C, Si, Cu, Mn, and Al wherein the composition comprisesfrom about 96.80 to about 98.10 percent by weight iron, from about 0.10to about 0.30 percent by weight carbon, from about 0.80 to about 1.15percent by weight silicon, from about 0.50 to about 0.65 percent byweight copper, from about 0.20 to about 0.50 percent by weightmanganese, and from about 0.30 to about 0.60 percent by weight aluminum,wherein the composition is substantially free of chromium.

Additional aspects of the present invention include articles comprisingthe hydrogen sulfide resistant steel compositions provided by thepresent invention.

Other embodiments, aspects, features, and advantages of the inventionwill become apparent to those of ordinary skill in the art from thefollowing detailed description and the appended claims.

DETAILED DESCRIPTION

In the following specification and the claims, which follow, referencewill be made to a number of terms, which shall be defined to have thefollowing meanings.

The singular forms “a”, “an”, and “the” include plural referents unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about” and “substantially”, are not to be limited tothe precise value specified. In at least some instances, theapproximating language may correspond to the precision of an instrumentfor measuring the value. Here and throughout the specification andclaims, range limitations may be combined and/or interchanged, suchranges are identified and include all the sub-ranges contained thereinunless context or language indicates otherwise.

In one embodiment, the present invention provides a corrosion resistantsteel composition which is especially resilient in hydrogensulfide-containing environments, such as oil refineries where refinerycomponents such as heat exchangers, distillation columns, conduits, andcondensers are subject to exposure to hot organic fluids comprisinghydrogen sulfide. The compositions provided by the present invention areanticipated to be useful as well in natural gas and crude oil productionequipment such as pumps, well bore casings and storage vessels. In oneembodiment, the present invention provides an article comprising one ormore of the steel compositions disclosed herein, the article being avessel which may be used to contain mixtures comprising hydrocarbons andhydrogen sulfide. In one such embodiment, the vessel may be used as acomponent of a system used to recover hydrocarbons from ahydrocarbon-containing reservoir, for example a well bore casing or agas liquid separator.

Crude oil and intermediates produced in refineries from crude oil arefrequently complex mixtures of organic and inorganic materials. Suchmixtures present special corrosion risks in the presence of hydrogensulfide. In addition, the sulfur containing materials of such mixturesare believed to be important sources of hydrogen sulfide as the mixturesare heated during in various refining steps.

Those of ordinary skill in the art will appreciate that various crudeoil and natural gas production operations attending the recovery ofhydrocarbon resources from a hydrocarbon reservoir frequently entail thehandling of hot fluids comprising naturally occurring hydrogen sulfidepresent in the reservoir as well as other corrosive species present inthe reservoir.

The present invention provides corrosion resistant steel compositionswhich are relatively low cost relative to highly alloyed steels favoredbecause of their resistance to hydrogen sulfide induced corrosion. Inaddition, the corrosion resistant steel compositions provided by thepresent invention provide additional enhancements such as being weldablewithout having to rely upon post-weld heat treatments to assure weldintegrity, a property not shared by typical highly alloyed steels whichhave carbon equivalent values (CE) above 0.6 which renders themsusceptible to weld embrittlement in the absence of post-weld heattreatment. As will be appreciated by those of ordinary skill in the art,post-weld heat treatment can be a laborious and expensive process.

As noted, in one embodiment, the present invention provides a steelcomposition comprising the elements Fe, C, Si, Cu, and Mn wherein thecomposition comprises from about 96.80 to about 99.00 percent by weightiron, from about 0.10 to about 0.30 percent by weight carbon, from about0.20 to about 1.40 percent by weight silicon, from about 0.50 to about1.50 percent by weight copper, and from about 0.20 to about 1.00 percentby weight manganese, wherein the composition is substantially free ofchromium, and wherein the composition contains less than 0.1 percent byweight nickel, molybdenum, or tungsten.

Although not wishing to be bound by any particular theory, it isbelieved that the various elemental components (Fe, C, Si, Cu, Mn, Al)of the compositions provided by the present invention interact in suchas way such that each component must be present within the rangespecified in order for the composition to be effective in resistingsulfidic corrosion. Thus, compositions provided by the present inventionmust contain from about 96.80 to about 99.00 percent by weight iron withthe elements carbon, silicon, copper and manganese being present in theranges specified above, and the compositions contain less than 0.1percent by weight nickel, molybdenum, or tungsten. As used herein, theexpression “the compositions contain less than 0.1 percent by weightnickel, molybdenum, or tungsten” means that if any one or more of theelements Ni, Mo and W is present in a corrosion resistant steelcomposition provided by the present invention, that element is presentin an amount less than 0.1 percent by weight based on the total weightof the composition. As noted, the compositions provided by the presentinvention are substantially free of chromium. A composition provided bythe present invention which is substantially free of an element, forexample chromium or aluminum, may contain low levels of the element,however, the amount of the element present in the composition is toosmall to produce any effect on the sulfidic corrosion resistance of thecomposition. Thus, it is believed, and the data confirm, that thepresence chromium will have no effect on the sulfidic corrosionproperties of compositions provided by the present invention when it ispresent in an amount less than about 0.20 percent by weight. Table Ibelow illustrates specific compositions of the invention which aresubstantially free of chromium.

TABLE I Corrosion Resistant Steel Compositions Entry Fe C Si Cu Mn 1a98.00 0.22 0.20 0.65 0.23 1b 98.25 0.22 0.40 0.60 0.25 1c 98.25 0.240.60 0.5 0.30 1d 96.8 0.28 1.39 1.35 0.15 1e 96.85 0.26 1.25 1.40 0.22 †All values are percent by weight based on a total weight of thecomposition.

In one embodiment, the present invention provides an article comprisinga corrosion resistant steel composition comprising the elements Fe, C,Si, Cu, and Mn wherein the composition comprises from about 96.80 toabout 99.00 percent by weight iron, from about 0.10 to about 0.30percent by weight carbon, from about 0.20 to about 1.40 percent byweight silicon, from about 0.50 to about 1.50 percent by weight copper,and from about 0.20 to about 1.00 percent by weight manganese, whereinthe composition is substantially free of chromium, and wherein thecomposition contains less than 0.1 percent by weight nickel, molybdenum,or tungsten. In one embodiment, the article is a component of an oilrefinery, for example a pipe, a heat exchanger, or a distillation columnIn various embodiments, such an article exhibits a corrosion rate ofless than 15 mpy when exposed to hydrogen sulfide according CorrosionTest Method No. 1 of the Experimental Part of this disclosure.

In one embodiment, the present invention provides a corrosion resistantsteel composition which is substantially free of chromium and containsless than 0.1 percent by weight nickel, molybdenum, or tungsten, andcomprises aluminum in addition to comprising from about 96.80 to about99.00 percent by weight iron, from about 0.10 to about 0.30 percent byweight carbon, from about 0.20 to about 1.40 percent by weight silicon,from about 0.50 to about 1.50 percent by weight copper, and from about0.20 to about 1.00 percent by weight manganese. In one or moreembodiments, the aluminum is present in an amount corresponding to fromabout 0.20 to about 0.60 percent by weight. In one embodiment, thepresent invention provides an article comprising such a corrosionresistant steel composition comprising aluminum. In one embodiment, thearticle is a component of an oil refinery, for example a pipe, a heatexchanger, or a distillation column In various embodiments, such anarticle exhibits a corrosion rate of less than 15 mpy when exposed tohydrogen sulfide according Corrosion Test Method No. 1 of theExperimental Part of this disclosure. Table II below provides specificexamples of such corrosion resistant steel compositions.

TABLE II Corrosion Resistant Steel Compositions Entry Fe C Si Cu Mn Al2a 97.61 0.22 1.07 0.50 0.20 0.20 2b 98.00 0.15 0.70 0.52 0.22 0.25 2c97.75 0.24 0.61 0.50 0.15 0.45 2d 96.85 0.20 1.20 0.75 0.33 0.52 2e96.91 0.29 1.27 0.65 0.25 0.58 2f 97.98 0.22 0.61 0.54 0.20 0.32 2g97.80 0.24 0.48 0.58 0.35 0.49 † All values are percent by weight basedon a total weight of the composition

In one embodiment, the present invention provides a corrosion resistantsteel composition comprising about 97.5 percent by weight iron, about0.2 percent by weight carbon, about 1.0 percent by weight silicon, about0.4 percent by weight aluminum, about 0.4 percent by weight Mn, andabout 0.6 percent by weight copper, wherein the composition issubstantially free of chromium, and wherein the composition containsless than 0.1 percent by weight nickel, molybdenum, or tungsten.

In one embodiment, the present invention provides a corrosion resistantsteel composition comprising the elements Fe, C, Si, Cu, and Mn whereinthe composition comprises from about 96.80 to about 99.00 percent byweight iron, from about 0.10 to about 0.30 percent by weight carbon,from about 0.20 to about 0.40 percent by weight silicon, from about 0.50to about 1.00 percent by weight copper, and from about 0.20 to about1.50 percent by weight manganese, wherein the composition issubstantially free of chromium and aluminum, and wherein the compositioncontains less than 0.1 percent by weight nickel, molybdenum, ortungsten. In one embodiment, the present invention provides an articlecomprising such a corrosion resistant steel composition. In oneembodiment, the article is a component of an oil refinery, for example apipe, a heat exchanger, or a distillation column In various embodiments,such an article exhibits a corrosion rate of less than 15 mpy whenexposed to hydrogen sulfide according Corrosion Test Method No. 1 of theExperimental Part of this disclosure. Table III below provides specificexamples of such corrosion resistant steel compositions. In oneembodiment, such corrosion resistant steel compositions comprise carbonin an amount corresponding to from about 0.15 to about 0.25 percent byweight. See for example the compositions of Entries 3a-3c of Table III.In one embodiment, such corrosion resistant steel compositions comprisesilicon in an amount corresponding to from about 0.25 to about 0.35percent by weight. See for example the compositions of Entries 3a-3c ofTable III.

TABLE III Corrosion Resistant Steel Compositions Substantially Free ofCr and Al Entry Fe C Si Cu Mn 3a 98.00 0.15 0.25 0.65 0.23 3b 98.25 0.200.30 0.60 0.30 3c 98.15 0.24 0.35 0.55 0.40 3d 97.05 0.26 0.38 1.35 0.753e 96.82 0.29 0.40 1.45 1.00 † All values are percent by weight based ona total weight of the composition.

In yet another embodiment, the present invention provides a corrosionresistant steel composition comprising the elements Fe, C, Si, Cu, Mn,and Al wherein the composition comprises from about 96.80 to about 98.10percent by weight iron, from about 0.10 to about 0.30 percent by weightcarbon, from about 0.80 to about 1.15 percent by weight silicon, fromabout 0.50 to about 0.65 percent by weight copper, from about 0.20 toabout 0.50 percent by weight manganese, and from about 0.30 to about0.60 percent by weight aluminum, wherein the composition issubstantially free of chromium, and wherein the composition containsless than 0.1 percent by weight nickel, molybdenum, or tungsten. See,for example, the compositions of Entries 4a-4e of Table IV. In one ormore embodiments, the present invention provides an article comprisingsuch a corrosion resistant steel composition. In one or moreembodiments, such an article is a component of an oil refinery, forexample a pipe, a heat exchanger, or a distillation column In one ormore embodiments, such an article exhibits a corrosion rate of less than15 mpy when exposed to hydrogen sulfide according to Corrosion TestMethod No. 1 of the Experimental Part of this disclosure

TABLE IV Corrosion Resistant Steel Compositions Entry Fe C Si Cu Mn Al4a 97.61 0.22 1.05 0.55 0.20 0.30 4b 97.50 0.20 1.00 0.52 0.22 0.35 4c97.45 0.24 0.95 0.50 0.25 0.40 4d 96.95 0.26 0.90 0.65 0.48 0.45 4e96.80 0.29 1.23 0.60 0.50 0.58 † All values are percent by weight basedon a total weight of the composition

Compositions provided by the present invention are characterized by a“carbon equivalence” (CE) value. As previously noted, a CE valueprovides an indicator of whether or not an article comprising a givensteel composition will require post-welding heat treatment in order toreduce the susceptibility of the article to corrosion in the heataffected zone (HAZ) in and around the weld. CE values may be calculatedas shown in the Experimental Part of this disclosure. Typically, when acorrosion resistant steel composition exhibits a CE value in a rangefrom about 0.44 to about 0.54, such a CE value may be taken as arelatively reliable indicator that an article made from such a corrosionresistant steel composition may not require post weld heat treatment inone or more applications.

In one embodiment, the present invention provides a corrosion resistantsteel composition which is substantially free of chromium and aluminum,which contains less than 0.1 percent by weight nickel, molybdenum, ortungsten, and which comprises from about 96.80 to about 99.00 percent byweight iron, from about 0.10 to about 0.30 percent by weight carbon,from about 0.20 to about 1.40 percent by weight silicon, from about 0.50to about 1.50 percent by weight copper, and from about 0.20 to about1.00 percent by weight manganese, wherein the composition has a carbonequivalence (CE) value in a range from about 0.44 to about 0.54. In oneor more embodiments, such compositions have a carbon equivalence (CE)value in a range from about 0.44 to 0.50.

In an alternate embodiment, the present invention provides a corrosionresistant steel composition which is substantially free of chromium andaluminum, which contains less than 0.1 percent by weight nickel,molybdenum, or tungsten, and which comprises from about 96.80 to about99.00 percent by weight iron, from about 0.10 to about 0.30 percent byweight carbon, from about 0.20 to about 0.40 percent by weight silicon,from about 0.50 to about 1.50 percent by weight copper, and from about0.2 to about 1.00 percent by weight manganese, wherein the corrosionresistant steel composition has a carbon equivalence (CE) value in arange from about 0.44 to 0.54. In one or more embodiments, suchcompositions have a carbon equivalence (CE) value in a range from about0.44 to 0.50.

Experimental Part General Methods

The experimental steels compositions were prepared and processed at GEGlobal Research facilities. All steel compositions were cast by vacuuminduction melting using elemental raw materials. After casting, eachingot was preheated at 1100° C. for approximately 90 minutes beforeforging sideways in one pass to a thickness of 0.25 inches. Care wastaken to avoid decarburization by wrapping the ingots in stainless steelfoil prior to heat treatment and forging. After air-cooling to ambienttemperature, the forged parts were grit blasted and rinsed in alcohol.The exterior surfaces of the forged articles were then ground on asurface grinder to provide oxide free surfaces. The resulting parts werecold rolled to a thickness of approximately 0.100 inch in severalpasses, each cold rolling pass providing a reduction in thickness ofapproximately 10%. The cold rolled parts were then annealed at 870° C.for 30 minutes and subsequently cooled at approximately 0.4° C./min tobelow 650° C. All heat treatments were carried out under an argonatmosphere. Following the annealing step, the parts were again gritblasted and rinsed in alcohol. The parts were then cold rolled to sheetshaving a thickness of approximately 0.060 inches. Each cold rolling passprovided a reduction in thickness of about 10%. Once the steelcompositions had been processed into sheets, they were sectioned intocorrosion coupons (approximately 0.75 inch×1 inch× 1/16 inch). Thesurfaces of the corrosion coupons, including edge surfaces, wereindividually ground as before. In preparation for corrosion testing, thedimensions (width, length and thickness) of each test coupon weremeasured, each coupon was weighed three times and the weights anddimensions were recorded, and the surface areas of the coupons werecalculated. Coupons were weighed again immediately before and aftercorrosion testing. Corrosion tests were carried out by a provider ofcorrosion testing services DNV-Columbus, Dublin, Ohio and used a testprotocol approved by the inventors, at times herein referred to asCorrosion Test Method No. 1. The corrosion tests were performed in a 4-LHastelloy autoclave fitted with ports for gas purging and pressuregauges. The coupons were hung from a glass coupon tree that wassuspended from the lid of the autoclave. Each coupon was electricallyisolated from all other coupons and from the autoclave itself. For eachbatch test, the autoclave was charged with 2.5 liters of oil (naphthenicdistillate heavy oil HR 1200). After sealing the autoclave, the oil waspurged at ambient temperature with nitrogen for 24 hours beforeswitching the purging gas to the corrosion test gas (10% H₂S+90% N₂). Anoverhead pressure of approximately 30-40 psi was applied to the exitinggas. The temperature was then raised to the test temperature (600° F.)and the coupons were exposed to the hydrogen sulfide-containingenvironment at 600° F. for 72 hours.

After testing, the coupons were cleaned with toluene to remove the oiland weighed to determine the level of scale formation during testing. Ininterpreting test data the following analysis was applied. A weight gainwould show that corrosion product scale had formed on the coupon wasadherent and did not spall, a weight loss would indicate the formationof a scale that spalls (detaches) as it forms. Following exposure to thetest conditions, the coupons were cleaned of any corrosion products(scale) using ASTM G01 standard inhibited hydrochloric acidic solution(Rodine 213). Lastly, the coupons were lastly weighed three more timesand the average final weight was calculated. The averaged final weightwas used to calculate the corrosion rate by mass loss.

The corrosion rate (CR) was calculated using the ASTM G1 formula inwhich the weight loss of the coupon during the exposure time in theautoclave was converted into linear penetration rate (mpy or “mils peryear”) by dividing each coupon mass loss by the exposed area of thecoupon, by the density of the alloy and by the exposure time.

${C\; {R({mpy})}} = \frac{{Wi} - {Wf}}{{Area} \times {Density} \times {Time}}$

In the equation above, Wi is the initial weight (mass) of the coupon,and Wf is the final mass of the coupon. In the case of the experimentalalloys, in which the density was not available, an estimated density of7.85 g/cm³ was used.

Actual compositions of the steels were determined by ion chromatographyand combustion analysis.

EXAMPLE 1

A 985 g batch of experimental steel (GE reference SUL9) comprisingapproximately 97.78 percent by weight iron, approximately 0.21 percentby weight carbon, approximately 0.26 percent by weight silicon,approximately 0.54 percent by weight copper, and approximately 0.96percent by weight manganese was prepared and transformed into testcoupons which were subjected to corrosion testing as described in thegeneral methods section. The composition contained measurable, butnegligible amounts of Mo (0.023%), Al (0.003%), Cr (0.16%), S (0.001%),V (0.0015%) and Ni (0.072%) totaling approximately 0.26 percent byweight. Coupons prepared using the steel composition of this Example 1exhibited a corrosion rate (CR) of 12.8±0.4 mpy, a rate equivalent to orsuperior to that observed for a highly alloyed steel API P91 (SeeComparative Example 1).

EXAMPLE 2

A 985 g batch of experimental steel (GE reference SUL40) comprisingapproximately 97.50 percent by weight iron, approximately 0.20 percentby weight carbon, approximately 1.01 percent by weight silicon,approximately 0.37 percent by weight aluminum, approximately 0.57percent by weight copper, and approximately 0.35 percent by weightmanganese was prepared and transformed into test coupons which weresubjected to corrosion testing as described in the general methodssection. The composition contained measurable, but negligible amounts ofMo (0.0032%), Cr (0.00077%), S (0.0025%), V (trace), Ni (0.0013%), andZn (trace) totaling approximately 0.01 percent by weight. Couponsprepared using the steel composition of this Example 2 exhibited acorrosion rate (CR) of 10.6±0.5 mpy, a rate equivalent to or superior tothat observed for alloyed steel API P91 (See Comparative Example 1).

COMPARATIVE EXAMPLE 1

Test coupons were cut from a commercially available API P91 steel pipe(GE reference P91) comprising approximately 89.39 percent by weightiron, approximately 0.12 percent by weight carbon, approximately 0.34percent by weight silicon, approximately 0.92 percent by weightmolybdenum, approximately 8.4 percent by weight chromium, approximately0.44 percent by weight manganese, and about 0.21 percent by weightvanadium. The API P91 steel contained measurable, but negligible amountsof Al (0.01%), S (0.001%), N (0.042%), and Ni (0.13%), totalingapproximately 0.18 percent by weight, and was essentially free ofcopper. The test coupons which were subjected to corrosion testing asdescribed in the general methods section. Coupons prepared using thesteel composition of this Comparative Example 1 exhibited a corrosionrate (CR) of 11±0.7 mpy.

COMPARATIVE EXAMPLE 2

Test coupons were cut from a commercially available steel pipe made ofthe alloy A106 (GE reference A106) comprising approximately 98.22percent by weight iron, approximately 0.25 percent by weight carbon,approximately 0.25 percent by weight silicon, approximately and 1.01percent by weight manganese. The A106 steel contained measurable, butnegligible amounts of Al (0.029%), Counter rotating (0.18%), S (0.002%),and Ni (0.06%), totaling approximately 0.27 percent by weight, and wasessentially free of copper. The test coupons were subjected to corrosiontesting as described in the general methods section. Coupons preparedusing the steel composition of this Comparative Example 2 exhibited acorrosion rate (CR) of 16.9±1.4 mpy.

COMPARATIVE EXAMPLE 3

A 985 g batch of experimental steel (GE reference SUL33) comprisingapproximately 98.08 percent by weight iron, approximately 0.20 percentby weight carbon, approximately 0.90 percent by weight silicon,approximately 0.321 percent by weight aluminum, and approximately 0.36percent by weight manganese was prepared and transformed into testcoupons which were subjected to corrosion testing as described in thegeneral methods section. The composition contained measurable, butnegligible amounts of Mo (0.03%), Cr (0.0775%), Cu (0.023%), S(0.0035%), V (trace), Ni (0.0025%), and Zn (trace) totalingapproximately 0.14 percent by weight. Coupons prepared using the steelcomposition of this Comparative Example 3 exhibited a corrosion rate(CR) of 13.4±0.7 mpy.

COMPARATIVE EXAMPLE 4

A 150 kg batch of experimental steel (GE reference SUL41) was preparedby a commercial allow producer (Sophisticated Alloys, Inc., Butler, Pa.,USA) using the general procedure provided herein as directed by theinventors. The alloy comprised approximately 97.83 percent by weightiron, approximately 0.18 percent by weight carbon, approximately 1.02percent by weight silicon, approximately 0.45 percent by weightaluminum, and approximately 0.52 percent by weight manganese wasprepared and transformed into test coupons which were subjected tocorrosion testing as described in the general methods section. Thecomposition contained measurable, but negligible amounts of N (trace)and was essentially free of Cu. Coupons prepared using the steelcomposition of this Comparative Example 4 exhibited a corrosion rate(CR) of 14.2±0.4 mpy.

Data for all embodiments of the invention and comparative examples isgiven in Table V.

TABLE V CE-2 CE-1 Ex.-1 CE-3 EX. 2 CE-4 Alloy Element A106 P91 SUL9SUL33 SUL40 SUL41 Fe 98.22 89.39 97.78 98.08 97.50 97.83 C 0.25 0.120.205 0.201 0.196 0.18 Si 0.25 0.34 0.26 0.90 1.01 1.02 Mo 0.92 0.0230.03 0.0032 0 Al 0.029 0.01 0.0028 0.321 0.3675 0.45 Cr 0.18 8.4 0.160.0775 0.00077 0 Mn 1.01 0.44 0.96 0.3565 0.3525 0.52 Cu 0.536 0.0230.565 0 S 0.002 0.001 0.0012 0.0035 0.0025 0 N 0.042 0 <0.0005 <0.0005<0.0005 V 0.21 0.0015 0.000025 7.5E−06 0 Ni 0.06 0.13 0.072 0.00250.0013 0 Zn — 0.000052 0.000024 0 Total 100.00 100.00 100.00 100.0099.99 100.00 CE^(†) 0.50 2.16 0.48 0.43 0.46 0.44 Average 16.9 11 12.813.4 10.6 14.2 Corrosion (mpy) 95% 1.4 0.7 0.4 0.7 0.5 0.4 confidenceInterval± ^(†)CE = Carbon Equivalence

The data illustrate the surprising resistance of the steel compositionsprovided by the present invention to sulfidic corrosion relative to thecontrol samples (Comparative Examples 1-4). In addition, the steelcompositions provided by the present invention had carbon equivalence(CE) values below 0.50, a good indicator that such steel compositionsneed not be heat treated following welding. Carbon equivalence iscalculated as shown below in Equation (1).

CE=% C+(% Mo+% Cr+% V)/5+(% Si+% Mn)/6+% Cu/15   (1)

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal language of the claims.

What is claimed is:
 1. A steel composition comprising the elements Fe,C, Si, Cu, and Mn wherein the composition comprises from about 96.80 toabout 99.00 percent by weight iron, from about 0.10 to about 0.30percent by weight carbon, from about 0.20 to about 1.40 percent byweight silicon, from about 0.50 to about 1.50 percent by weight copper,and from about 0.20 to about 1.00 percent by weight manganese, whereinthe composition is substantially free of chromium, and wherein thecomposition contains less than 0.1 percent by weight nickel, molybdenum,or tungsten.
 2. The composition according to claim 1, further comprisingaluminum.
 3. The composition according to claim 2, wherein the aluminumin an amount corresponding to from about 0.20 to about 0.60 percent byweight.
 4. The composition according to claim 1, having a carbonequivalence (CE) value in a range from about 0.44 to about 0.55.
 5. Thecomposition according to claim 1, having a carbon equivalence (CE) valuein a range from about 0.44 to 0.50.
 6. The composition according toclaim 1 comprising about 97.5 percent by weight iron, about 0.2 percentby weight carbon, about 1.0 percent by weight silicon, about 0.40percent by weight aluminum, about 0.4 percent by weight Mn, and about0.6 percent by weight copper, wherein the composition contains less than0.1 percent by weight nickel, molybdenum, or tungsten.
 7. An articlecomprising the composition of claim
 1. 8. An article according to claim7 and having a corrosion rate of less than 15 mpy when exposed tohydrogen sulfide according Corrosion Test Method No. 1 of thisdisclosure.
 9. A steel composition comprising the elements Fe, C, Si,Cu, and Mn wherein the composition comprises from about 96.80 to about99.00 percent by weight iron, from about 0.10 to about 0.30 percent byweight carbon, from about 0.20 to about 0.40 percent by weight silicon,from about 0.50 to about 1.50 percent by weight copper, and from about0.2 to about 1.00 percent by weight manganese, wherein the compositionis substantially free of chromium and aluminum, and wherein thecomposition contains less than 0.1 percent by weight nickel, molybdenum,or tungsten.
 10. The composition according to claim 9, wherein carbon ispresent in an amount corresponding to from about 0.15 to about 0.25percent by weight.
 11. The composition according to claim 9, whereinsilicon is present in an amount corresponding to from about 0.25 toabout 0.35 percent by weight.
 12. The composition according to claim 9,having a carbon equivalence (CE) value in a range from about 0.44 to0.54.
 13. The composition according to claim 9, having a carbonequivalence (CE) value in a range from about 0.44 to 0.50.
 14. Thecomposition according to claim 9 comprising about 97.78 percent byweight iron, about 0.21 percent by weight carbon, about 0.26 percent byweight silicon, about 0.54 percent by weight copper and about 0.96percent by weight manganese, wherein the composition contains less than0.1 percent by weight nickel, molybdenum, or tungsten.
 15. An articlecomprising the composition of claim
 9. 16. An article according to claim15 and having a corrosion rate of less than 15 mpy when exposed tohydrogen sulfide according to Corrosion Test Method No. 1 of thisdisclosure.
 17. A steel composition comprising the elements Fe, C, Si,Cu, Mn, and Al wherein the composition comprises from about 96.80 toabout 98.10 percent by weight iron, from about 0.10 to about 0.30percent by weight carbon, from about 0.80 to about 1.15 percent byweight silicon, from about 0.50 to about 0.65 percent by weight copper,from about 0.20 to about 0.50 percent by weight manganese, and fromabout 0.30 to about 0.60 percent by weight aluminum, wherein thecomposition is substantially free of chromium, and wherein thecomposition contains less than 0.1 percent by weight nickel, molybdenum,or tungsten.
 18. An article comprising the steel composition of claim17.
 19. The article according to claim 18, wherein and having acorrosion rate of less than 15 mpy when exposed to hydrogen sulfideaccording to Corrosion Test Method No. 1 of this disclosure.
 20. Thearticle according to claim 19, wherein the article is a component of anoil refinery.
 21. The article according to claim 19, wherein the articleis a vessel which may be used to contain mixtures comprisinghydrocarbons and hydrogen sulfide.
 22. The article according to claim19, wherein the vessel may be used as a component of a system used torecover hydrocarbons from a hydrocarbon-containing reservoir.
 23. Thearticle according to claim 22, wherein the vessel is a well bore casing.24. The article according to claim 22, wherein the vessel is agas-liquid separator.